1. Field of the Invention
The present invention relates to a digital-television receiving antenna, and more particularly, to a broadband planar digital-television receiving antenna.
2. Description of the Prior Art
In the past, a TV program operator broadcasts analog signals to receivers through ultra-high-frequency (UHF) or very-high-frequency (VHF) channels. Analog signals are easily interfered during transmission, so that picture clarity, noise and ghost-image reductions are insufficient. Also, transmitting analog signals requires a considerable frequency bandwidth, which decreases the efficiency of frequency utilization. In contrary, a digital TV (DTV) system transmits TV programs with digital signals, which can be compressed to increase the efficiency of frequency utilization. Moreover, a receiver of the DTV system can process debugging or error corrections for digital signals, so that the DTV system has higher quality in video and audio, and more channel numbers. Now, the DTV system has been developed in three main standards, DVB (Digital Video Broadcasting) by European Broadcast Union (EBU), ATSC (Advanced Television Systems Committee) by US, and ISDB (Integrated Services Digital Broadcasting) by Japan. The DVB standard has been authorized by European Telecommunications Standard Institute (ETSI), and includes substandards of DVB-S (satellite), DVB-C (cable) and DVB-T (terrestrial). According to the DVB standard, a DVB system encodes video and audio signals with MPEG-2 coding technology, modulates the signals with coded orthogonal frequency division multiplexing (COFDM), and uses a frequency bandwidth of 8 MHz (23.5 Mbps). A DVB-T system can establish a single frequency network (SFN) for increasing available frequency resources, provide interactive TV functions, and reduce a multipath effect. In order to improve mobile receiving efficiency of a vehicle DVB-T receiver, advanced channel estimation is applied and a dual-antenna is used for receiving radio waves and performing diversity combining, and accordingly, circuit complexity, hardware cost, and power consumption cannot be decreased. A DTV receiving antennal is a fundamental equipment of a common DTV tuner. Most DTV receiving antennas are monopole antennas, which have large sizes and insufficient bandwidths. Therefore, a planar DTV receiving antenna having a wide bandwidth is desired.
TW patent No. 521,455 discloses a small planar DTV antenna for receiving DTV signals. However, the antenna of TW patent No. 521,455 has a large volume, so that it is inconvenient.
Referring to FIG. 2, which illustrates a schematic diagram of an antenna 2 of the prior art. The antenna 2 includes a dielectric substrate 20, a radiating plate 21, a slit 24, feeding points 25, 26, and a feeding coaxial cable 27. The dielectric substrates 20 can be a copper clad laminate substrate, or be made of film or rubber. The radiating plate 21 is formed on the dielectric substrates 20 by printing or etching. The radiating plate 21 is formed as a bar shape, and includes a first long edge 211 and a second long edge 212 corresponding to the first long edge 211. A length of the slit 24 is approximately equal to a width W of the radiating plate 21. The slit includes terminals 241 and 242. The terminal 241 is at about a center of the first long edge 211, and the terminal 142 is also at about the center of the second long edge 212. The slit 24 separates the radiating plate 21 into a first sub-plate 22 and a second sub-plate 23. The feeding points 25 and 26 are near the first long edge 211, and at the first sub-plate 22 and the second sub-plate 23, respectively. The feeding coaxial cable 27 is utilized for transmitting/receiving signals, and includes a core conductor 271 connected to the feeding point 25 and a grounding conductor 272 connected to the feeding point 26. Note that, the slit 24 is formed without any bending, or is perpendicular to the first long edge 211 and the second long edge 212.
Referring to FIG. 3, which illustrates a schematic diagram of an antenna 3 of the prior art. The antenna 3 includes a dielectric substrate 30, a radiating plate 31, a slit 34, feeding points 35, 36, and a feeding coaxial cable 37. The dielectric substrates 30 can be a copper clad laminate substrate, or be made of film or rubber. The radiating plate 31 is formed on the dielectric substrates 30 by printing or etching. The radiating plate 31 is formed as a bar shape, and includes a first long edge 311 and a second long edge 312 corresponding to the first long edge 311. The length of the slit 34 is approximately equal to the width W of the radiating plate 31. The slit includes terminals 341 and 342. The terminals 341 and 342 are at a distance (about 60 mm) from centers of the first long edge 311 and the second long edge 312. The slit 34 separates the radiating plate 31 into a first sub-plate 32 and a second sub-plate 33. The feeding points 35 and 36 are near the first long edge 311, and at the first sub-plate 32 and the second sub-plate 33, respectively. The feeding coaxial cable 37 is utilized for transmitting/receiving signals, and includes a core conductor 371 connected to the feeding point 35 and a grounding conductor 372 connected to the feeding point 36. Note that, the slit 34 is formed without any bending, or is perpendicular to the first long edge 311 and the second long edge 312.